Implantation processes for straining transistor channels of semiconductor device structures and semiconductor devices with strained transistor channels

ABSTRACT

The present invention includes methods for stressing transistor channels of semiconductor device structures. Such methods include the formation of so-called near-surface “nanocavities” adjacent to the source/drain regions, forming extensions of the source/drain regions adjacent to and including the nanocavities, and implanting matter of a type that will expand or contract the volume of the nanocavties, depending respectively upon whether compressive strain is desirable in transistor channels between the nanocavities, as in PMOS field effect transistors, or tensile strain is wanted in transistor channels, as in NMOS field effect transistors, to enhance carrier mobility and transistor speed. Semiconductor device structures and semiconductor devices including these features are also disclosed.

FIELD OF THE INVENTION

The present invention relates generally to methods for straining transistor channels of semiconductor device structures to improve device performance. More specifically, the present invention relates to methods in which impurities and thermal processing are applied to strain the transistor channels. The present invention also relates to methods for fabricating semiconductor devices and to semiconductor devices.

BACKGROUND OF RELATED ART

Improvements in hole mobility have been recognized in PMOS devices (i.e., metal-oxide-semiconductor (MOS) devices with n-type, or n-doped, substrates and p-type charge, or hole, carriers), or transistors, by compressively straining the channels of such devices. Similar improvements in electron mobility have been realized in NMOS devices (i.e., MOS devices with p-type, or p-doped, substrates and n-type charge or electron, carriers), or transistors, when the channels thereof experience tensile strain. Enhanced carrier mobility may be used as a means to improve transistor speed and performance.

A number of techniques have been researched to compressively stress PMOS regions, including the inclusion of a strained layer of silicon-germanium (SiCe) within the source/drain regions to compressively stress the channel region between the source and drain, which results in an increase in hole mobility of up to 50%. Strained silicon layers have also been fabricated on relaxed silicon-germanium layers in the channel regions of NMOS devices to create uniaxial tensile stress in the channel region between the source and drain to enhance electron mobility and increase the speed of NMOS transistors.

When silicon germanium is used, a layer of silicon-germanium is formed, typically by ultra-high vacuum chemical vapor deposition (CVD) techniques. The layer of silicon-germanium is then capped with a thinner silicon film. Lattice mismatches between the relaxed silicon-germanium layer and the silicon capping layer generate the desired tensile stress. Unfortunately, the ultra-high vacuum CVD techniques that have been used to fabricate silicon-germanium layers are extremely expensive and, thus, less conducive to use in large-scale semiconductor device fabrication processes.

A number of other experimental techniques for stressing channel regions of semiconductor device structures have also been developed. Tensile strain has been generated in the channels of NMOS devices by using silicon carbide (SiC) in the source/drain regions. Semiconductor device structures have also been bent (which may, e.g., be effected in packaging and encapsulation) to stress the transistor channels. In addition, semiconductor device structures have been fabricated with stress-inducing silicon nitride capping layers.

It would be desirable to develop a process by which transistor channels of semiconductor device structures may be stressed economically and on a scale that is suitable for incorporation into semiconductor device fabrication.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, in which various features of embodiments of the present invention are depicted:

FIG. 1 depicts an embodiment of an intermediate semiconductor device structure in which strained transistor channels may be formed;

FIGS. 2-10 illustrate an embodiment of a method for straining transistor channels of a semiconductor device structure; and

FIGS. 11-16 show another process for straining transistor channels of a semiconductor device structure in accordance with another embodiment of the present invention.

DETAILED DESCRIPTION

The present invention includes methods for straining the semiconductor channels of transistors. Such methods include the formation of so-called near-surface “nanocavities” adjacent to the source/drain regions of a transistor, and implanting and embedding elements within the nanocavities of a type that will expand or contract (i.e., strain) the volumes of the nanocavities, depending respectively upon whether a resulting compressive strain in the transistor channel between the nanocavities is desirable, as in PMOS transistors (e.g., PMOS field effect transistors, or PFETs), or a resulting tensile strain is wanted, as in NMOS transistors (e.g., NMOS field effect transistors, or NFETs), to enhance carrier mobility and transistor speed.

With reference to FIG. 1, an embodiment of an intermediate semiconductor device structure 10 that includes a plurality of transistors 20, 20′ is shown. Transistors 20 and 20′ are formed adjacent to a surface 14 of a semiconductor substrate 12. The term “semiconductor substrate,” as used in herein, includes, without limitation, full or partial wafers of semiconductive material (e.g., silicon, gallium arsenide, indium phosphide, etc.), semiconductor-on-insulator (SOI) type substrates (e.g. silicon-on-ceramic (SOC), silicon-on-glass (SO), silicon-on-sapphire (SOS), etc.), and any other suitable fabrication substrates. In the illustrated embodiment, which should not be considered to limit the scope of the present invention, each transistor is disposed between a pair of isolation structures 16, which may comprise dielectric regions, such as the various configurations of shallow trench isolation (STI) structures known in the art.

Each transistor 20, 20′ may include spaced-apart source 22, 22′ and drain 24, 24′ regions formed in semiconductor substrate 12 at surface 14. A gate region insulator layer 26 is disposed on surface 14 and is positioned laterally between source 22, 22′ and drain 24, 24′. One or more conductive layers 27 are located on gate region insulator layer 26 and form a conductive element 27 of the gate 21, 21′ of transistor 20, 20′. An oxide film 28 (e.g., a silicon dioxide film formed by thermal oxidation, low temperature oxidation, or other suitable process, etc.) coats the top and side walls of conductive element 27 and forms a portion 29 of a gate cap 31 on conductive element 27.

A silicon nitride film is formed over oxide film 28. The silicon nitride film is then patterned, as known in the art to form a “hard” mask. Silicon nitride is removed from side walls of each gate 21, 21′ and from locations over surface 14 that are immediately laterally adjacent to the side walls of each gate 21, 21′. The results of such patterning are a nitride cap 30 a, which comprises another part of gate cap 31, over each gate 21, 21′ and a nitride mask 30 b, which resides on portions of gate region insulator layer 26 that overlie isolation structures 16 and locations where source/drain regions 22, 22′, 24, 24′ are to be formed. Regions 26 e of gate region insulator layer 26 that are located laterally adjacent to each gate 21, 21′ are not covered by nitride mask 30 b.

Disposable side wall spacers 32, which have been fabricated by known processes (e.g., blanket deposition of a suitable material, such as polysilicon, and use of a spacer etch), are located adjacent to the side walls of each gate 21, 21′. Notably, each disposable side wall spacer 32 is formed directly on a region 26 e of gate region insulator layer 26. The material from which disposable side wall spacers 32 are formed may be removable with selectivity over, or at a faster rate than, the material of nitride cap 30 a and nitride mask 30 b.

In the depicted embodiment, transistor 20 is an NFET, or a transistor that includes source/drain regions 22, 24 that are doped with n-type, or negative charge carrier or electron-donating, dopants, or impurities (e.g., phosphorus (P), arsenic (As), antimony (Sb), etc.). Transistor 20′ is a PFET, which includes source/drain regions 22′, 24′ that are doped with p-type, or positive charge carrier or hole-generating, dopants, or impurities (e.g., boron (B), aluminum (Al), etc.). Ion implantations of appropriate impurities for source/drain regions 22, 24 (n+ for NFET) and source/drain regions 22′, 24′ (p+ for PFET) are successively carried out using appropriate photomasks for PFET and NFET regions, respectively, as practiced in standard CMOS fabrication processes.

The illustrated features of semiconductor device structure 10 and of transistors 20 and 20′ thereof may be fabricated by any suitable, known processes.

An embodiment of a method for straining source/drain regions 22, 22′ and 24, 24′ of transistors 20 and 20′ and, consequently, the channel regions of transistors 20 and 20′, is shown in FIGS. 2 trough 10.

As shown in FIG. 2, disposable side wall spacers 32 are removed from transistors 20, 20′. Disposable side wall spacers 32 (see FIG. 1) may be selectively removed by any suitable process, such as with an etchant that removes the material of side wall spacers 32 with selectivity over nitride cap 30 a and oxide film 28 portion 29 of gate cap 31. Once disposable side wall spacers 32 are removed, regions 26 e (see FIG. 1) of gate region insulator layer 26 previously shielded by disposable side wall spacers 32 are exposed and may be removed. Such removal may be effected as part of the same process as the removal of disposable side wall spacers 32, or as part of a subsequent process. Removal of portions of gate region insulator layer 26 results in the exposure of surface 14 of semiconductor substrate 12 at locations 12 e that are laterally adjacent to source/drain regions 22, 22′ and 24, 24′ at locations that are laterally adjacent to gate 21, 21′.

As shown in FIG. 3, a thin region of substrate material is removed from semiconductor substrate 12 at locations 12 e (see FIG. 2) where surface 14 is exposed. Such material removal, which forms nano-trenches 34 in semiconductor substrate 12, may be effected in a controlled manner to a predetermined depth (e.g., to a depth of 200 Å or thereabout). Without limiting the scope of the present invention, material may be removed from semiconductor substrate 12 by a controlled etch process.

An amorphous semiconductor material 36 (e.g., amorphous silicon) may then be introduced into nano-trenches 34 and, thus, into contact with the exposed portions of semiconductor substrate 12, as shown in FIG. 4. The newly introduced amorphous semiconductor material 36 may protrude beyond a plane in which surface 14 is located; thus, a thickness of amorphous semiconductor material 36 may exceed the depth to which material was removed from semiconductor substrate 12 (e.g., 200 Å or thereabout). Any suitable process may be used to introduce amorphous semiconductor material 36 into nano-trenches 34 In some embodiments, a suitable deposition process (e.g., chemical vapor deposition (CVD), atomic layer deposition (ALD), etc.) may be used to form an amorphous semiconductor film (not shown). When a blanket deposition process is used, any portions of the amorphous semiconductor film that overlie nitride caps 30 a and/or nitride mask 30 b may, of course, be removed by a suitable process; for example, with a wet etchant.

As shown in FIG. 5, a surface 38 (see FIG. 4) of amorphous semiconductor material 36 may be oxidized to form an oxide film 40 (e.g., a silicon dioxide film) on each quantity of amorphous semiconductor material 36 residing primarily within a nano-trench 34. Any suitable oxidation process, including, but not limited to, a low temperature oxidation technique, may be employed. The resulting oxide film 40 may have a thickness of about 50 Å to about 100 Å.

After an oxide film 40 has been formed on each quantity of amorphous semiconductor material 36 (see FIG. 5), as FIG. 6 depicts, a mask 42 of known, suitable type (e.g., a photomask, etc.) may be formed so as to shield and prevent implantation of helium (He) into regions of semiconductor device structure 10 where implantation is not desired. As depicted, source/drain regions 18, which are confined between isolation structures 16, are exposed through mask 42.

With mask 42 in place, a shallow helium (He) ion implantation process may be conducted. By way of example and not by way of limitation, He ion implantation may be effected by known processes at a dose of at least about 3×10²⁰ ions per cm³, which facilitates the confinement and distribution of subsequently implanted ions to within a depth of about 200 Å of surface 14.

Semiconductor device structure 10 is then subjected to rapid thermal processing (RTP), or a rapid thermal anneal (RTA), of a known type (see, e.g., Rangan, S., et al., “Formation and characterization of multi-layered nanocavities in silicon with cascade helium implantation/anneal,” Proceedings, 6^(th) Int'l Conf. on Solid State and Integrated-Circuit Technology, 2:1360-1363 (2001), Ntsoenzok, E., et al., “Helium implant depth dependence on thermal growth of nanocavities in silicon,” Proceedings, 7^(th) Int'l Conf. on Solid State and Integrated-Circuit Technology, 3:2382-2386 (2002), the disclosures of both of which are hereby incorporated herein, in their entireties, by this reference) to form nanocavities 44, 44′ from amorphous semiconductor material 36 that remains within nano-trenches 34.

FIG. 7 shows he formation of n-source/drain extensions 48 (i.e., lateral extensions of source/drain regions 22, 24, which may be considered to form a part of their corresponding active-device region) in each NFET 20 while each PFET 20′ is shielded from such processing (e.g., by way of a mask 46, such as a photomask or the like, as illustrated). N-type impurities 47 are implanted into semiconductor substrate 12 through oxide film 40 and each nanocavity 44 by known processes.

As FIG. 8 illustrates, equivalent processes may be used to form p-source/drain extensions 48′ (i.e., lateral extensions of source/drain regions 22′, 24′, which may be considered to form a part of their corresponding active-device region) in each PFET 20′ as each NFET 20, or at least the nanocavities 44 thereof is shielded (e.g., by mask 46′, as illustrated). Again, an implantation process is employed with parameters that implant p-type impurities 47′ to a location that exceeds the depth of each nanocavity 44′.

The implantation processes for the stress inducing elements and for the impurities are controlled in such a way that the impurities are implanted more deeply into amorphous semiconductor material 36 than the stress inducing elements. For example, implantation of the stress inducing elements may be confined to a peak depth of about 100 Å into amorphous semiconductor material 36 and to a distribution of about 100 Å from each peak. By establishing impurity profiles that are deeper than the profiles of the implanted stress inducing elements and the resulting strained portions of source/drain regions 22, 22′, 24, 24′, low leakage junction characteristics of the source/drain regions 22, 22′, 24, 24′ may be preserved.

Once source/drain extensions 48 (see FIG. 7) and 48′ (see FIG. 8) have been formed, semiconductor device structure 10 may optionally be subjected to rapid thermal processing, the parameters (e.g., temperature, duration, etc.) of which facilitate at least partial activation of the implanted impurities. In some embodiments, an RTA at a temperature of up to about 900° C. could be carried out for about one second to about ten seconds to achieve partial activation of the implanted impurities.

Stress inducing elements are now selectively implanted in regions 48, 22, 24 and 48′, 22′, 24′ for each type of device (i e., NFET 20 and PFET 20′, respectively). Sidewall spacers may then be fabricated by known processes (e.g., by depositing a suitable material, such as a silicon nitride, silicon oxide, silicon oxynitride or the like, use of spacer etch techniques, etc.).

In addition to implanting impurities into source/drain extensions 48 and 48′, stress inducing elements 49 (see FIG. 9), 49′ (see FIG. 10) may also be implanted into source/drain extensions 48 and 48′, as well as into source/drain regions 22, 22′, 24, 24′. In this regard, hydrogen species or a mixture of hydrogen molecules (H₂) and argon (Ar) may be implanted into source/drain extensions 48 and, optionally, into source/drain regions 22, 24 of each NEST 20 as shown in FIG, 9. Such “hydrogen implantation” may be effected as known in the art, such as at a dose of at least about 3×10²⁰ molecules per cm³ for each implanted species (e.g., hydrogen, argon, both hydrogen and argon, etc.), and limited to a depth that is within about 150 Å from surface 14.

Similarly, as illustrated in FIG. 10, oxygen species may be implanted into source/drain extensions 48′ and, optionally, into source/drain regions 22′, 24′ of each PFET 20′, as shown in FIG. 10. Without limiting the scope of the present invention, oxygen implantation may be effected as known in the art, at a dose of at least about 3×10²⁰ molecules per cm³ and limited to a depth that is within about 150 Å from surface 14.

Rapid thermal processing of appropriate parameters (e.g., temperature, duration, etc.) may then be conducted to establish the desired profiles for source/drain regions 22, 22′, 24, 24′, as known in the art, as well as establish the desired profiles for source/drain extensions 48 and 48′ of source/drain regions 22, 22′, 24, 24′. Additionally, the RTP induces uniaxial tensile stress (in the direction in which charge carriers (i.e., holes) flow) in the channel of each NFET 20 (see FIG. 9), in the form of recrystallization of amorphous silicon in source/drain regions 22, 24 and/or extensions 48 thereof at or near surface 14 which decreases, or shrinks, the volume of each recrystallized area. In addition, the RTP generates compressive stress in the channel (i.e., the semiconductor material between source/drain regions 22′ and 24′) of each PFET 20′ (see FIG. 10), in the form preferential oxidation of source/drain regions 22′, 24′ and/or extensions 48′ hereof at helium-induced bubbles at or near surface 14, which increases, or expands, e volume of each preferentially oxidized region. The results of such stress are, respectively, uniaxial tensile strain in the transistor channel between the volume-contracted, or shrunk, source/drain regions 22, 24 or extensions 48 thereof in each NFET 20 and compressive strain in the transistor channel between the volume-expanded source/drain regions 22′, 24′ or extensions 48′ thereof of each PET 20′.

Another embodiment of a method of the present invention is illustrated in FIGS. 11 through 16. After implanting impurities into source/drain regions 122, 124, disposable side wall spacers 32 (see FIG. 1) and underlying regions 26 e of gate region insulator layer 26 (see FIG. 1) are removed to expose locations 12 e of semiconductor substrate 12 that are laterally adjacent to the side walls of gates 21, 21′, as illustrated in FIG. 11.

As shown in FIG. 12, material is removed from semiconductor substrate 12 at locations 12 e (see FIG. 11) where surface 14 is exposed. Such material removal, which forms nano-trenches 134 in semiconductor substrate 12, may be effected in a controlled manner to a predetermined depth (e.g., to a depth of 500 Å or thereabout). Without limiting the scope of the present invention, material may be removed from semiconductor substrate 12 by a controlled etch process.

Turning to FIG. 13, known epitaxial processes may then be used to form a film 136 of semiconductor material (e.g., crystalline silicon, etc.) on each exposed location 12 e of semiconductor substrate 12. Each semiconductor film 136 may have a thickness of about 1,000 Å or less.

As shown in FIG. 14, a surface 138 (see FIG. 13) of each semiconductor film 136 may be oxidized to form an oxide film 140 (e.g., a silicon dioxide film) on each semiconductor film 136 residing primarily within a nano-trench 134. Any suitable oxidation process, including, but not limited to, a low temperature oxidation technique, may be employed. The resulting oxide film 140 may have a thickness of about 50 Å to about 100 Å.

FIG. 15 shows the formation of n-source/drain extensions 148 (i.e., lateral extensions of source/drain regions 122, 124, which may be considered to form a part of their corresponding active-device region) in each NFET 120 while each PFET 120′, isolation structures 16, and any other regions of semiconductor device 110 where implantation is not desired are shielded from such processing (e.g. by way of a mask 146, such as a photomask or the like, as illustrated). Stress inducing elements (e.g., argon and hydrogen molecules) (not shown) are implanted into source/drain regions 122, 124 and semiconductor film 136 through gate region insulator layer 26 and oxide film 140. Such implantation is effected at a dose of at least about 3×10²⁰ molecules per cm³.

As FIG. 16 illustrates, equivalent processes may be used to form p-source/drain extensions 148′ (i.e., lateral extensions of source/drain regions 122′, 124′, which may be considered to form a part of their corresponding active-device region) i each PFET 120′ as each NET 120, or at least each semiconductor film 136 thereof, isolation structures 16, and other regions of semiconductor device 1 10 where implantation is not desired are shielded (e.g., by mask 146′, as illustrated). Stress inducing elements and p-type impurities (not shown) are implanted into source/drain regions 122′, 124′ and semiconductor films 136 through gate region insulator layer 26 and oxide film 140, respectively. Such implantation for stress inducement is effected at a dose of at least about 3×10²⁰ molecules per cm³ for each type of element implanted.

The implantation processes for the stress inducing elements and for the impurities are controlled in such a way that the impurities are implanted more deeply into each semiconductor film 136 than the stress inducing elements. In some embodiments of a method of the present invention, implantation of the stress inducing elements may be confined to a peak depth of about 100 Å into each semiconductor film 136 and to a lateral distribution of about 100 Å from each peak. By establishing impurity profiles that are deeper than the profiles of the implanted stress inducing elements and the resulting strained portions of source/drain regions 122, 122′, 124, 124′, low leakage junction characteristics of the source/drain regions 122, 122′, 124, 124′ may be preserved.

Once source/drain extensions 148 and 148′ have been formed, semiconductor device structure 110 may be subjected to rapid thermal processing, the parameters (e.g., temperature, duration, etc.) of which facilitate local oxidation/recrystallization of silicon (LOCOS) and at least partial activation of the implanted impurities, as well as form nanocavities (not shown) from semiconductor films 136 and establish the desired profiles for source/drain regions 122, 122′, 124, 124′ and their extensions 148 and 148′. Such rapid thermal processing may be effected by known RTA processes. In some embodiments, the RTA may be conducted at a temperature of about 1,000° C. for about one second to about ten seconds.

Additionally, the RTP induces tensile stress in each NFET 120, which occurs due to recrystallization and/or formation of epitaxial silicon in source/drain regions 122, 124 and/or extensions 148 thereof at or near surface 14. The recrystallization and/or formation of epitaxial silicon decreases, or shrinks, the volume of each recrystallized area, which, in turn, applies tensile stress to material between each pair of recrystallized and/or epitaxially formed regions. In addition, the RTP generates compressive stress in the channel of each PFET 120′, in the form preferential oxidation of source/drain regions 122′, 124′ and/or extensions 148′ thereof at helium-induced bubbles at or near surface 14. Oxidation increases, or expands, the volume of each preferentially oxidized region and compresses material between the preferentially oxidized regions, which, in turn, applies compressive stress to material between each pair of oxidized regions. The results of such stress are, respectively, tensile strain in the transistor channels between source/drain regions 122, 124 or extensions 148 thereof in each NFET 120 and compressive strain in the transistor channels between source/drain regions 122′, 124′ or extensions 148′ thereof of each PFET 120.

Once process flow according to embodiments of the present invention has occurred, further processing of semiconductor device structures 10, 110 may be effected, as known in the art, to fabricate complete semiconductor devices.

Embodiments of semiconductor device structures and semiconductor devices according to the present invention include features such as the source/drain regions 22, 22′, 24, 24′, nanocavities 44, 44′, and source/drain extensions 48, 48′, 148, 148′ shown in FIGS. 10 and 16.

Although the foregoing description contains many specifics, these should not be construed as limiting the scope of the present invention, but merely as providing illustrations of some of the presently preferred embodiments. Similarly, other embodiments may be devised which do not depart from the spirit or scope of the present invention. Features from different embodiments may be employed in combination. The scope of the invention is, therefore, indicated and limited only by the appended claims and their legal equivalents, rather than by the foregoing description. All additions, deletions and modifications to the invention as disclosed herein which fall within the meaning and scope of the claims are to be embraced thereby. 

1. A method for compressively stressing a transistor channel of a PMOS transistor, comprising introducing matter that expands a volume of at least portions of source/drain regions between which the transistor channel is located.
 2. The method of claim 1, wherein introducing comprises implanting oxygen species into at least the portions of the source/drain regions.
 3. The method of claim 1, wherein introducing comprises implanting helium species into at least the portions of the source/drain regions.
 4. A method for tensilely stressing a transistor channel of an NMOS transistor, comprising introducing matter that facilitates contraction of a volume of at least a portions of source/drain regions between which the transistor channel is located.
 5. The method of claim 4, wherein introducing includes introducing helium species into at least the portions of the source/drain regions.
 6. The method of claim 4, wherein introducing includes introducing hydrogen molecules into at least the portions of the source/drain regions.
 7. The method of claim 6, wherein introducing further includes introducing argon species into at least the portions of the source/drain regions.
 8. The method of claim 4, further comprising effecting a rapid thermal process.
 9. A method for stressing transistor channels of a semiconductor device structure, comprising: forming nanocavities near a surface of the semiconductor device structure and laterally between a gate stack and its corresponding source/drain regions; introducing conductivity dopants into extension regions of a semiconductor substrate of the semiconductor device structure that are at least adjacent to the nanocavities; activating the conductivity dopants; introducing stress inducing elements into the extension regions; treating at least the stress inducing elements to stress at least semiconductor material located between the nanocavities.
 10. The method of claim 9, wherein forming nanocavities includes forming nanocavities covered with oxide films.
 11. The method of claim 9, wherein forming nanocavities comprises forming nanocavities that are recessed about 500 Å beneath a surface of the semiconductor substrate and that have thicknesses of about 1,000 Å or less.
 12. The method of claim 11, wherein forming nanocavities comprises forming nanocavities covered with oxide films having thicknesses of about 50 Å to about 100 Å.
 13. The method of claim 9, wherein forming nanocavities comprises epitaxially forming semiconductor material.
 14. The method of claim 13, wherein activating and treating are effected simultaneously.
 15. The method of claim 9, wherein forming nanocavities comprises: forming amorphous semiconductor material; patterning the amorphous semiconductor material; introducing matter into the remaining portions of the amorphous semiconductor material; and subjecting at least the amorphous semiconductor material and the matter to rapid thermal processing.
 16. The method of claim 15, wherein introducing matter comprises implanting helium into the remaining portions of the amorphous semiconductor material.
 17. The method of claim 16, wherein implanting helium includes implanting helium no deeper than about 200 Å below the surface.
 18. The method of claim 15, wherein activating and treating are effected separately.
 19. The method of claim 18, wherein introducing conductivity dopants and activating the conductivity dopants are effected before introducing stress inducing elements and treating at least the stress inducing elements.
 20. The method of claim 9, wherein activating and treating include rapid thermal processing.
 21. The method of claim 9, wherein introducing stress inducing elements comprises introducing oxygen species into the extension regions of at least one PMOS transistor.
 22. The method of claim 9, wherein introducing stress inducing elements comprises introducing at least one of hydrogen species and argon species into the extension regions of at least one NMOS transistor.
 23. The method of claim 9, wherein introducing stress inducing elements comprises introducing the stress inducing elements to a depth of no more than about 150 Å below the surface.
 24. A semiconductor device structure, comprising: a semiconductor substrate; at least one PMOS transistor including: a transistor gate; a pair of source/drain regions flanking the transistor gate; a nanocavity located near a surface of the semiconductor substrate, laterally between each active-device region and Me transistor gate; and an extension of each active-device region encompassing an adjacent nanocavity, a transistor channel between the pair of source/drain regions and the extensions being compressively strained.
 25. The semiconductor device structure of claim 24, wherein a base of each nanocavity is recessed about 500 Å beneath the surface of the semiconductor substrate and each nanocavity has a thickness of about 1,000 Å or less.
 26. The semiconductor device structure of claim 24, wherein at least one of the pair of source/drain regions and the extensions are preferentially oxidized.
 27. A semiconductor device structure, comprising: a semiconductor substrate; at least one NMOS transistor including: a transistor gate; a pair of source/drain regions flanking the transistor gate; a nanocavity located near a surface of the semiconductor substrate, laterally between each active-device region and the transistor gate; and an extension of each active-device region encompassing an adjacent nanocavity, tensile strain being present in a transistor channel between the pair of source/drain regions and the extensions.
 28. The semiconductor device structure of claim 27, wherein a base of each nanocavity is recessed about 500 Å beneath the surface of the semiconductor substrate and each nanocavity has a thickness of about 1,000 Å or less.
 29. The semiconductor device structure of claim 27, wherein at least one of the pair of source/drain regions and the extensions comprise crystallized or recrystallized semiconductor material. 